The invention relates to an aircraft fuselage.
Generally speaking, aircraft fuselages comprise an outer skin that is stiffened by way of a backing structure and that in the vertical direction of the fuselage delimits an upper passenger cabin or an above-floor region and a lower cargo hold or below-floor region. The backing structure usually comprises stringers that extend in the longitudinal direction of the fuselage, and frame elements that extend in the circumferential direction of the fuselage. The passenger cabin and the cargo hold each comprise a floor framework, wherein the cabin floor framework is supported on the backing structure in the cargo hold.
Conventionally, the outer skin and the backing structure are made from metal materials such as aluminium alloys. However, present-day fuselage concepts provide for the metal materials to be replaced by fiber-composite materials, in particular carbon-fiber-reinforced plastics (CFRPs). Because with equal stiffness, fiber-composite materials feature a lighter weight. However, fiber-composite materials have a failure behavior under mechanical load that differs from the failure behavior of metal materials. While the metal materials have high ductility and thus in the case of overload absorb energy under plastic deformation, the fiber-composite materials are brittle so that in the case of overload a sudden total failure with only little energy absorption occurs.
However, in the case of a survivable crash, in other words if a commercial aircraft crashes from a low height, irrespective of the materials used it has to be ensured that the passenger cabin remains intact or almost intact and consequently survival of the passengers is ensured. In order to achieve this, the aircraft fuselage needs to provide corresponding energy absorption in the region of its cargo hold.
DE 10 2007 030 026 A1 shows a structural component for an aircraft fuselage that combines a frame element with a cargo-hold transverse member, wherein the transverse member has greater stiffness than the frame element. In this arrangement the frame element is used to reinforce the outer skin and is curved in an arc-shaped manner corresponding to an inner contour of the outer skin. The transverse member element transversely interconnects two arc portions of the frame element and absorbs mechanical loads on the structure to a greater extent than do said arc portions. Since the transverse member transversely interconnects the arc portions of the frame element, it is further removed from the outer skin, when viewed in the vertical direction of the fuselage, than the frame element. In the case of overload of the outer skin, first the frame element breaks and absorbs some of the impact energy. Since the stiffness of the transverse member is greater than that of the frame element, said transverse member does not break at the same time as the frame element, but instead in a manner stepped in time under the influence of the energy reduced by the breaking of the frame element. Thus the aircraft is decelerated in a stepped manner.
From DE 10 2008 042 452 A1 a fiber-composite component for energy absorption in the event of a crash is known, which fiber-composite component between its CFRP laminate layers comprises at least one integrated metal foil layer that is corrosion resistant vis-a-vis the CFRP laminate layers. This fiber-composite component combines both advantages of the different materials, namely the high strength including the light weight of the CFRP laminate layers with the high ductility of the metal.
From US 2009/0206202 A1 for energy absorption in the event of a crash it is known to support cargo-hold transverse members by way of almost vertical fiber-composite supports in the vertical direction of the fuselage on a backing structure of the aircraft fuselage, wherein the U-shaped fiber-composite supports by means of a multitude of laminate layers arranged in a stepped manner comprise quasi-wedge-shaped lateral limbs which in the case of overload acting on the aircraft fuselage are intended to be sheared off in a stepped manner.
Further state of the art is shown in FR 2 936 218 A1.